Food allergy is a detrimental immunoreaction in susceptible individuals that is caused by ingestion of an allergy-inducing substance in a food and can cause dermatitis, asthma, digestive-tract obstacle, anaphylactic shock, etc. Food allergy is primarily a so-called type I allergy, i.e. an immunological disorder mediated by IgE antibodies in which IgE antibodies react with food allergens taken inside the body. The number of food-allergy patients has been increasing in recent years and the phenomenon of food allergy causes serious problems in medical fields and in the food industry.
Allergy-inducing foods include eggs, milk, meat, fish, the crustaceans and mollusks, cereals, legumes and nuts, fruits, vegetables, gelatin, yeast (beer) etc. Similarly, ovoalbumin, ovomucoid, lysozyme, casein, beta-lactoglobulin, alpha-lactoalbumin, gluten, alpha-amylase inhibitor, etc. are known as allergy-inducing food constituents.
The diagnosis of food allergies is one field where many deficiencies still exist, regardless of the development of various tests. In many cases, the patients themselves notice a connection between their symptoms and certain allergens, for example by observing an immediate adverse reaction upon ingestion of the suspected allergen or by eliminating and re-introducing the source of allergens. A detailed anamnesis is therefore often very helpful in establishing a diagnosis.
Diagnosis of food allergy is performed in several, partly complementary ways. In addition to an anamnesis, the diagnosis can further be supported by in vivo measurements and in vitro assays. As in vivo technique a skin test with food allergen extracts is most common. Sometimes an oral provocation is necessary to determine which food components are the causative agents of the observed allergy. Methods for developing food products with a favorable allergy profile require double blind, placebo-controlled food challenge tests. The most common in vitro tests are RAST and ELISA. In these assays, extracts of potentially allergic, antigenic material are immobilized to a solid phase (e.g. Sepharose, magnetic particles, polystyrene plates, etc.). After incubation of the solid phase with serum of a patient, the binding of specific IgE antibodies is usually measured.
In particular the ELISA method suffers several drawbacks. For example the method cannot always detect allergens that food allergy patients are sensitive to. In other words, they cannot always detect substances that are recognized by IgE antibodies of the patients. Also the method can only detect known allergens, and a single allergen per method. Further the method using single antigen-detecting antibodies are not applicable to inspection of allergy-inducing foods containing no known antigen (e.g. a method using a single antibody prepared by exposure to ovalbumin localized in egg white is not applicable to inspection of egg yolk and for example egg yolk mayonnaise, etc.). The method using single antigen-detecting antibodies are not applicable to inspection of the processed foods, because they cannot detect denatured or molecule-modified allergens.
Thus many allergens have been identified and in some cases isolated and characterized down to molecular levels. In practice, however, it is often enough to identify a particular food stuff as source of allergens, e.g. cow milk containing several known allergenic proteins.
When it comes to provocation tests problems arise in specific situations, e.g. where the allergic reaction is either delayed, very diffuse or part of a complex of clinical symptoms. In the first case, when the reaction is delayed, it becomes difficult to associate the problems with the particular food causing them. Often, the symptoms resemble the symptoms of common problems such as headache, fatigue and joint pains. It is also possible that the same substances produce different reactions or at least fail to produce an identical reaction every time. It is understandable that the establishing of a diagnosis is both difficult, time-consuming and often frustrating for both the physician and the patient.
Besides this, in critically ill patients a provocation test is the last thing a physician would want to do. Moreover, it will probably be impossible to reliably relate, and this is even more the case where infants, and more in particular critically ill infants are concerned, a clinical symptom or complaint to a true allergic response.
Takagi et al. (2003) Biol. Pharm. Bull. vol 26(2), p 252 describe the application of human FcεRI α-chain-transfected RBL-2H3 cells for detecting receptor bindable serum IgE. The transfected cells were sensitized with heat-inactivated serum from allergic patients and stimulated with anti-human IgE antibody. Ambivalent results were obtained in a β-hexosaminidase assay for determining degranulation in samples having different dilution of sera. No particular interest is directed at food allergy.
Aketami et al. (2001) Immunology Letters vol 75, p 185 correlated calcium concentration and degranulation measured by the β-hexosaminidase assay in a RB-2H3 cell system sensitized with serum specific for chicken egg albumin generated in mice.
Dibbern et al. J. Immumunological Methods, (2003) vol 274, p 37 describe RBL cells expressing the complete human FcεRI receptor. Degranulation of such cells sensitized with sera from peanut-sensitive patients upon activation with peanut allergens was measured by determining tritium labelled serotonin.